Cathode-ray tube having planar grid accelerator adjacent and on screen side of beam deflectors

ABSTRACT

A cathode-ray tube having a luminescent screen and deflecting means surrounding the path of an electron beam impinging on the screen deflecting the beam in two perpendicular directions. A planar grid electrode having a rectangular periphery is arranged between the screen and the deflecting means for producing a postacceleration field between the screen and the grid electrode. A correction rim is mechanically and electrically connected to the periphery of the grid electrode and is designed to extend beyond the grid electrode toward the screen. An electrode, separate from the grid electrode, is arranged adjacent to and electrically insulated from the grid electrode and extends in the direction toward said deflecting means to enclose the electron beam. The deflecting means is preferably a pair of parallel deflecting plates, each pair spaced from one another along the path of the electron beam and effective to deflect the electron beam in one perpendicular direction; the pair of plates nearest the screen being arranged within the separate electrode.

Unite States Patent 1 3,706,896 Schafiernicht et al. 1 Dec. 19, 1972 s41 CATHODE-RAY TUBE HAVING 3,376,447 4/1968 Petit ..3l3/86X PLANAR GRID ACCELERATOR ADJACENT AND ON SCREEN SIDE OF FOREIGN PATENTS OR APPLICATIONS BEAM DEFLECTORS 570,672 7/1945 GreatBritain ..313 78 [72] Inventors: Klaus Schaffernicht; Gottfried Schadlich, both of Ulm, Danube, Primary Bummer-Robert Sega] Attorney-Spencer & Kaye Germany [73] Assignee: Licentia Patent-Verwaltungs- ABS AC Frankfurt Germany A cathode-ray tube having a luminescent screen and [22] Filed: July 15, 1970 V deflecting means surrounding the path of an electron beam impinging on the screen deflecting the beam in [21] Appl 54883 two perpendicular directions. A planar grid electrode having a rectangular periphery is arranged between 0 Foreign Application priority m the screen and the deflecting means for producing a post-acceleration field between the screen and the July 16, 1969 Germany P 19 36 229.9 grid electrode A correction rim is mechanically and electrically connected to the periphery of the grid UaS- Cl- 313/18, electrode and is designed to extend beyond the [51} Int. Cl. ..H01 29/80, H01 29/82 electrode toward the screen An electrode, separate [58] Field of Search ..313/82, 69 C, 70 C, 78, 83, f the grid electrode is arranged adjacent to and 313/86 electrically insulated from the grid electrode and extends in the direction toward said deflecting means to References Cited enclose the electron beam. The deflecting means is preferably a pair of parallel deflecting plates, each UNITED STATES PATENTS pair spaced from one another along the path of the 2,093,876 9/1937 Von Ardenne ..3l3/80 electron a and effective t d fl t th electron 3,250,942 5/1966 Yoshida et al ..313/82 X beam in one perpendicular direction; the pair of plates 3,143,681 8/ 1964 Schlesinger ..3l3/83 SP nearest the screen being arranged within the separate 2,936,399 5/1960 Zaphiropoulos... ..3 I 3/86 X electrode 3,154,710 10/1964 Parker.... ..313/86 X 3,240,972 3/1966 Law ..3l3/79 2 Claims, 3 Drawing Figures B ELECTRON 8 GUN PATENTED DEC 1 9 I972 fl' a ATTORNEYS.

BY w CATIIODE-RAY TUBE HAVING PLANAR GRID ACCELERATOR ADJACENT AND ON SCREEN SIDE OF BEAM DEFLECTORS BACKGROUND OF THE INVENTION The present invention relates to a cathode-ray tube (CRT) having a luminescent screen and means for deflecting an electron beam in two perpendicular deflection directions, as well as a planar grid electrode which is substantially perpendicular to the tube axis and disposed between the deflecting means and the screen for producing a post-acceleration field between the screen and the grid electrode: the latter being provided along its periphery with a correction rim extending over the grid electrode in the direction toward the luminescent screen.

It is known to provide a post-acceleration of the electron beam in oscillograph tubes between the deflecting means, which may be pairs of deflecting plates, and the screen by producing an electric post-acceleration field between a grid electrode disposed substantially perpendicularly to the tube axis and the luminescent screen. The grid electrode is preferably disposed closely behind the pair of deflecting plates nearest the screen so that the post-acceleration occurs over the longest permissible path of the electron beam. The grid electrode may either be planar or curved in one or two directions. This type of grid electrode is generally known under the term post-acceleration net. It must be substantially electron-permeable, and may consist of a thin foil, a crisscross grid, or of a parallel wire grid.

It has already been proposed to arrange a rim around the circumference of the grid electrode in such a postacceleration CRT as well. This rim extends beyond the CRT in the direction toward the screen and serves, inter alia, to correct geometric errors, particularly pincushion errors.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cathode-ray tube of the type described above which is improved with respect to the correction of deflection errors, and particularly correction of linearity errors.

This object and others are accomplished according to the present invention, by providing the grid electrode with a rectangular periphery, mechanically and electrically connecting the correction rim with the grid electrode, and disposing a further electrode closely adjacent the grid electrode in the direction toward the electron gun. This further electrode encloses the electron beam and is electrically insulated against the grid electrode.

In addition to substantial correction of the distortion errors, particularly a substantial correction of pincushion distortion and linearity errors, the CRT according to the present invention has the advantage of reducing the undesired brightening of the screen which results from slower secondary electrons emitted when the electron beam impinges on the grid electrode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the raster on the screen of a cathode-ray tube which exhibits strong pincushion distortion and linearity errors.

FIG. 2 is a schematic view of a raster on the screen of a cathode-ray tube utilizing the correction electrode of the present invention.

FIG. 3 is a schematic view showing a cathode-ray tube according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the raster on the screen of a cathoderay tube which exhibits strong pincushion distortion and linearity errors produced when the correction electrode of the present invention is not provided. FIG. 2 shows a raster on the screen of a cathode-ray tube which is provided with the correction electrode of the present invention.

FIG. 3 is a schematic view of an arrangement of a cathode-ray tube having a grid electrode 6, a further, or separate, electrode 2, and pairs of known deflecting plates 3 and 4 spaced along the electron beam path designated by arrow 7. The electrons are emitted from a known electron gun 8, and impinge on a known luminescent screen 9.

Electrode 6 is of the type generally known as a postacceleration net", and is constructed of a thin metal foil, or a crisscross or parallel wire grid. Any suitable electrically conductive material other than metal may be used as well.

The correction electrode 1 is disposed directly at the periphery of the grid electrode 6. It is constructed of an electrically conductive material and is mechanically and electrically connected with the frame of the grid electrode 6 in a well known manner so that it has the same electrical potential as the grid electrode 6.

According to a preferred embodiment of the present invention, the periphery of the grid electrode 6 and that of the correction electrode 1 has a rectangular shape; the side edges of the grid electrode and of the correction electrode extending substantially parallel to the two deflection directions of the pairs of deflecting plates 3 and 4 (see FIG. 3). It is particularly advantageous, as also shown in FIG. 3, if the edge of the portion of the correction electrode 1 which extends beyond the grid electrode 6 is bent in an oblique direction so that this edge becomes conically larger toward the screen 9. The height h (FIG. 3) of the edge of the correction electrode 1 facing the screen 9 advisably varies over the extent of its rectangular periphery, for example, in such a manner that the edges of the rim pointing toward the screen define a curve which is either concave or convex. By appropriate selection of the tilt angle a of the rim (FIG. 3), it is possible to influence the correction effect, whereas proper selection of the varying height h of the rim exerts a substantial influence on the correction in the corners of the frame.

According to a preferred embodiment of the present invention an electrode 2 is disposed between the gun 8 and the grid electrode 6. This electrode 2 is constructed of an electrically conductive material and is in the form of a sheath to enclose the electron beam. Advisably, the cross section of electrode 2 is also rectangular, and its inner dimensions should correspond to the cross section of the grid electrode 6.

The deflecting plates 3 are preferably disposed inside electrode 2, and the deflecting plates 4 disposed substantially between gun 8 and electrode 2. A simple structure can be achieved by employing the electrode 2 as the support member for the grid electrode 6 and the correction electrode 1; it being advisable to electrically separate the further electrode 2 from the grid electrode 6, which is done with the aid of an insulating intermediate member 5. Any suitable known electrical insulating material may be used for member 5. Such a structure according to the present invention has the advantage that a positive potential with respect to electrode 6 can be applied to the electrode 2. This is shown schematically in FIG. 3 by battery 10. The secondary electrons emitted when the electron beam impinges on, for example, the grid wires of the grid 6 are then attracted away by electrode 2, so that annoying brightening of the screen is substantially prevented. The electrode 2, moreover, acts as a shielding electrode to shield the deflecting plates 3 against the post-acceleration field. The shape of the electrode 2 has, furthermore, a slight influence on the distortion correction. It is thus possible to compensate production tolerances in the correction rim 1 by a suitable selection of the potential at the electrode 2.

Although the separate electrode 2 of the present invention is shown in theembodiment described above as being used with a cathode-ray tube having electrostatic deflection, it is to be understood that such an electrode can also be used with a cathode-ray tube having electromagnetic deflection.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. In a cathode-ray tube, the improvement comprising, in combination:

a. a luminescent screen;

b. deflecting means surrounding the path of an electron beam impinging on said screen for deflecting the beam in two perpendicular directions, said deflecting means including two pairs of deflecting plates, said pairs being spaced from one another along the path of the electron beam and each pair being effective to deflect the electron beam in one of said two perpendicular directions; c. a planar grid electrode, having a rectangula periphery, for producing a post-acceleration field between said screen and said grid electrode, said planar grid electrode being arranged substantially perpendicular to the tube axis in the path of the electron beam of said tube and being located adjacent said deflecting means and between said screen and said deflecting means; d. a correction rim mechanically, and electrically connected to the periphery of said grid electrode and extending beyond said grid electrode toward said screen, said rim expanding conically toward said screen and having a rectangular periphery, and the height of said correction rim varying along its rectangular periphery that faces said screen; and

e. an elongated hollow electrode, separate from said grid electrode, arranged adjacent to and electricall insulated from said grid electrode and exten ing in the direction oward said deflecting means and enclosing the path of the electron beam of said tube; f. said grid electrode and said correction rim being mechanically connected to said hollow electrode for support thereby, said hollow electrode being a sheath of rectangular cross section which is dimensioned to mate with the cross section of said grid electrode, and the pair of deflection plates nearest said screen being arranged at least partially within the sheath of said hollow electrode. 2. A cathode-ray tube as defined in claim 1, wherein a potential which is positive with respect to said grid electrode is applied to said separate electrode.

l060ll 0198 

1. In a cathode-ray tube, the improvement comprising, in combination: a. a luminescent screen; b. deflecting means surrounding the path of an electron beam impinging on said screen for deflecting the beam in two perpendicular directions, said deflecting means including two pairs of deflecting plates, said pairs being spaced from one another along the path of the electron beam and each pair being effective to deflect the electron beam in one of said two perpendicular directions; c. a planar grid electrode, having a rectangular periphery, for producing a post-acceleration field between said screen and said grid electrode, said planar grid electrode being arranged substantially perpendicular to the tube axis in the path of the electron beam of said tube and being located adjacent said deflecting means and between said screen and said deflecting means; d. a correction rim mechanically and electrically connected to the periphery of said grid electrode and extending beyond said grid electrode toward said screen, said rim expanding conically toward said screen and having a rectangular periphery, and the height of said correction rim varying along its rectangular periphery that faces said screen; and e. an elongated hollow electrode, separate from said grid electrode, arranged adjacent to and electrically insulated from said grid electrode and extending in the direction toward said deflecting means and enclosing the path of the electron beam of said tube; f. said grid electrode and said correction rim being mechanically connected to said hollow electrode for support thereby, said hollow electrode being a sheath of rectangular cross section which is dimensioned to mate with the cross section of said grid electrode, and the pair of deflection plates nearest said screen being arranged at least partially within the sheath of said hollow electrode.
 2. A cathode-ray tube as defined in claim 1, wherein a potential which is positive with respect to said grid electrode is applied to said separate electrode. 